Printing process employed in color photography



' usual however image in turn from the celluloid support to the final'transfer of the image Patented Dec. 20, 1932 UNITED" STATES PATENT OFFICE LESLIE WALTER OLIVER AND WILLIAM: GEORGE CLARE, LONDON, ENGLANI AS- SIGNORS TO COLOUR PHOTOGRAPHS (BRI ENGLAND, A BRITISH COMPANY TISH AND FOREIGN) LIMITED, OF LONDON,

PRINTING PROCESS EMPLOYED IN COLOR PHOTOGRAPHY No Drawing. Application filed June 2, 1931, Serial No. 541,686, and in Great Britain June 23, 1930.

This invention comprises improvements in or relating to printing processes employed in color photography.

The invention relates to, a process of the type in-which relief images obtained by differential hardening, by light or chemical ac tion, are formed upon colloid layers carried on suitable supports. I

A well known example of the above type of processand one with which the present invention is particularly concerned-is the so-called carbon or carbro process in which a picture in natural colors is obtained by printing from negatives taken through colored filters'on the complementary colors. Usually in carrying out such a process the following pro,-

cedure is adopted. The tissues, which con'-.

sist essentially of a paper base coated with a mixture of soluble gelatine and the appropriate coloring matter, are rendered sensitive to light by treatment with alkali dichromate solutions. After exposure, the tissues are soaked in water, squeegeed into contact with celluloid or other impervious supports and later immersed in warm water, when the paper backing and unexposed gelatine leaves the support and a colored image in hardened gelatine is left. The three images (which in a three-color process are colored respectively magenta, yellow and blue green) may now be dried on their celluloid supports and mounted in register. It is more to transfer each developed a final paper base. This transference s rendered possible by coating the celluloid with a thin layer of wax before mounting the carbon tissue thereon for development. Unless the wax is suitably chosen pigmented image is liable to leave the cellu loid support during. development (frill ng) and in those cases where such frilling does not occur it often proves difficult to effect from the celluloid to the final support. In those .cases where the transference is successful 'it is necessary to remove the wax from the surface of the transferred'im'age before the other images can be mounted thereon.

to carbon tissues dyed nr and applied the strength and toughness when wet. Accord-' ing to the above proposal there was no transference from one support to another after development, and the three-color pictures were thus made up of three superimposed" sheets ofcellophane each bearing one of the three-color components.

While the use of regenerated cellulose as a final support presents distinct advantages over celluloid, special means must beitaken in order that the resultant color picture may remain fiat under changing atmospheric conditions. Moreover, if it is desired to adjust the proportions of the constituent colors in the finished printfor example, to reduce the amount of yellow whilst leaving the other colors untouched-the presence in the finished picture of three isolating layers of cellophane render this operation difficult and uncertain in accomplishment and accordingly such color balancing must be fore the three tisues are mounted together.

The present invention provides a printing process of the type described (i. e. in which relief images obtained by differential hardening are formed on colloid layers) which is performed becharacterized by combining the use, as a support for the image during development, of regenerated-cellulose (particularly that known under the registered trade-mark Cellophane) or like material which is transparent. homogeneous, permeable to water, and retentive of its mechanical strength and toughness when 'wet, with the transference of the developed image from its regeneratedcellulose or like support to as paper. v

Thus according to the invention the advantages of using cellophane or the like as a supportduring development are retained. while the difficulties attendant upon the presanother base suchence of the cellophane sheets as part of the finalpicture are obviated.

In one method, according to the invention, of efiecting the transference of the image from the cellophane to the final support, the sheet of cellophane bearing the developed image is first soaked in water until fully swollen and is then mounted face downwards upon a piece of gelatine coated paper. A

dilute solution of gelatine can conveniently be used as the mountant. The sandwich is now dried partially or completely and is then immersed in a dilute solution of a gela tine hardening or tanning agent, for example dilute solutions of potash alum, chrome alum, formalin or acrolein. After a .few minutes immersion in such a solution, the cellophane can be readily separated from the paper support and the colored image will be found to be adhering firmly to the latter. Whilst the above procedure provides the simplest'means for accomplishing this transfer, it has been found that soaking of the dried sandwich in water alone is sufficient to enable the cellophane to be separated from the image. In this case, however, it is necessary to dry the sandwich almost completely and to soak in water solution for some considerable time before attempting to strip off the cellophane.

In general, in carrying out the invention an adhesiveis used in mounting. or treatment is applied to the mounted sandwich such that the'adhesion of the colored image to the chosen final support is rendered greater than its adhesion to the sheet of regenerated cellulose whereon it was developed.

It is to be understood that in carrying out the process according to this invention the final support need not necessarily be of paper; other materials such as ivory, glass. canvas, silk or metal may be employed. Where a metal surface is used as the final support the transferred image may provide a suitable relief for an etching process such as photogravure. Transference to the curved metal surfaces commonly used in photogravure is not practicable from semi-stiff water-impermeable development supports such as celluloid and in consequence it has up till now been common pract ce to develop the carbon image directly on to the metal. With such practice the production of suitable reliefs is entirely dependent on the skill of the operatives. However by employing as develop ment supports sheetsof flexible water-permeable material such as cellophane it is pos sible to determine the suitability of the reliefs before transferring them to the cylinders.

We claim: r

1. In a color-photographic printing process in which relief images obtained by differential hardening are formed on colloid layers, a method of transferringthe developed image from a temporary support of regenerated cellulose to a final base of another material which consists in soaking the image-bearing sheet in water until fully swollen, then mounting it face downwards upon the final support using a dilute solution of gelatine as a mountant, partially drying the sandwich, then immersing it in a dilute solution of a gelatine hardening agent, and finally stripping oif the development support.

2. In a color-photographic printing process in which relief images obtained by dif- 'ferential hardening are formed on colloid layers, a method of transferring the developed image from a temporary support of regenerated cellulose to a final base of another material which consists in soaking the image-bearing sheet in water until fully swollen, then mounting it face downwards upon the final support using a dilute solution of gelatine as a mountant, completely drying the sandwich, soaking it'in water and finally stripping off the development support.

3. In color photography a printing process which comprises developing, by differential hardening, a relief image on a colloid layer supported upon a sheet of regenerated cellulose, combined with transferring the developed image from its aforesaid regenerated cellulose support to'another and final base by first soaking the image-bearing sheet in water until fully swollen, then mounting it face downwards upon the final base using an adhesive solution as a mountant, then drying the sandwich thus formed, and finally stripping off the development support.

4. In color photography a printing process which comprises developing, by differential hardening, a relief image on a colloid layer supported upon a sheet of regenerated cellulose, combined with transferring the developed image from its aforesaid regenerated cellulose support to another and final base of gelatine-coated paper by first soaking the image-bearing sheet in water until fully swollen, then mounting it face downwards upon the gelatine-coated surface of the final base, drying the sandwich thus formed, and finally stripping off the development support.

5. In color photography a printing process which comprises developing, by differential hardening, a relief image on a. colloid layer supported by a sheet of cellophane, combined with transferring the developed image from its cellophane support to another and final base of paper by first soaking the cellophane sheet in water until fully swollen, then mounting it face downwards on the paper base using a dilute solution of gelatine as a mountant, drying the sandwich thus formed and finally stripping off the cellophane support.

In testimony whereof We have signed our names to this specification.

' LESLIE WALTER OLIVER.

WILLIAM GEORGE CLARE. 

